Exploring Time Capsule: WiFi 802.11n and the 5GHz Band
Earlier versions of the WiFi specification all used the 2.4GHz radio spectrum. The new 802.11n standard, supported in Time Capsule, the square AirPort Extreme, and recently shipping AirPort Express units, allows users to alternatively select the use of 5GHz channels. This segment, the third of six, compares the pros and cons of using this new section of frequencies, which can be both problematic and provide a major boost in speed.
Our real world testing of Time Capsule's WiFi performance suggested two findings. First, wireless networking performance can and will vary all over the map even without any obvious variables changing. This makes it difficult to accurately profile the speed of a wireless configuration. In comparison, file copy times over Ethernet or direct connections such as USB were easy to verify in additional follow-up tests. Actual results for wireless throughput will vary dramatically in relation to obvious sources of radio interference in addition to other sporadic factors that are harder to identify.
Second, users with multiple base stations should ideally connect the computers that will be making heavy use of file sharing to the base station actually hosting the shared drive. This requires some network planning, as client computers will attempt to connect to the base station supplying the strongest signal of all the base stations that are on the same network. In other words, locate the Time Capsule or AirPort Extreme hosting the share drive closest to the systems that will be using it the most, and use any additional base stations to extend the network signal elsewhere.
Next, evaluate the wireless network signal strength within AirPort Utility (below) to make sure there are no obvious sources of signal interference. This could include radio emitting devices such as cordless phones and microwave ovens, unnecessary Bluetooth devices that could be turned off, and any metal barriers that might obstruct the signal. Neighboring WiFi networks may also likely impede ideal connectivity, so if possible, experiment with different WiFi channel settings to situate your wireless network outside of the signal range used by other nearby networks.
802.11n WiFi and The 5 GHz Band
As noted earlier, with WiFi 802.11n on the AirPort Extreme and Time Capsule, you can set up your network to use a different set of frequencies all together by selecting "802.11n only (5GHz)" as the radio mode in Wireless settings (below). This isolates your network from interference from other 802.11b/g WiFi networks as well as any 2.5 GHz cordless phones, but of course prevents older 802.11b/g clients from connecting to your network, including most Macs earlier than 2007 and other WiFi b/g devices such as the iPhone or iPod Touch.
If you have both old and new wireless devices, you can cable (via Ethernet, below) a new 802.11n base station hosting a 5 GHz network to an older 802.11b/g base station configured to operate in the "802.11b/g compatible" 2.4 GHz band. This enables faster devices to connect at full speed with minimal interference, while also allowing older devices to connect to the same network through the older base station and interoperate together with every other device on the same network. This setup also prevents 802.11b/g devices from temporarily slowing down a 802.11n network as they transmit, which happens when using mixed devices on a 802.11n base station configured as "b/g compatible."
Incidentally, there is also an 802.11a standard, which is essentially 802.11g running in the 5 GHz band. All of Apple's 802.11n base stations and wireless cards now backwardly support 802.11a/b/g, but Apple never directly supported the earlier 802.11a standard in its products prior to 802.11n because 802.11a was largely intended for office deployments, where the downsides to the 5 GHz band could be more easily worked around. Which brings us to the potential drawbacks--and advantages--of using 5 GHz.
On Page 2 of 2: The Pros and Cons of 5 GHz; Use Wide Channels For a Big Boost.
The Pros and Cons of 5 GHz
As noted by Glenn Fleishman in the article Wi-Fi Networking News: 5 GHz or Bust, the 5 GHz band has much greater radio spectrum available; there are 12 non-overlapping channels, each with 20 MHz of bandwidth. The entire 2.4 GHz band is only 80 MHz wide, which only allows for three non-overlapping 20 MHz channels; while you can select any channel between 1 and 11 in the standard 2.4 GHz band, there is so much overlap between channels that only 1, 5, and 11 can really coexist in the same area without interference. When using 5 GHz, the base station selects the channel for you automatically.
However, 5 GHz is also a higher, shorter radio frequency, which means that at the same amount of radio transmission power, its radio waves propagate shorter distances than those of 2.4 GHz base stations. The 5 GHz band is also worse at penetrating solid objects such as wooden walls in a home (neither band can penetrate metal walls, such as lath and plaster walls using a metal mesh found in some older buildings). There are also power transmission restrictions that affect the use of the 5 GHz band. These factors combine to result in users likely seeing a significant drop in their signal range when using 5 GHz.
In our initial tests, switching to 5 GHz initially had no positive impact on wireless transmission speeds. In fact, it actually seemed to slow things down. However, Apple's 802.11n AirPort devices, including Time Capsule, support a wide channel mode when using 5 GHz that does make a big difference in network speed.
Use Wide Channels For a Big Boost
The greatest advantage to using 5 GHz is the ability to bond two channels together, which Apple calls "Use wide channels." (below) This allows the base station to grab twice as much radio bandwidth (40 MHz) and should be turned on by default when using the 5 GHz band. This will also boost the reported connection speed from 130 to 300 Mbit/sec, at the expense of possibly interfering with other nearby 5 GHz networks, giving up some signal range, and dropping compatibility with 802.11b/g devices.
However, once configured to use wide channels in the 5 GHz band (the setting hides behind the "Wireless Options..." button on the Wireless tab of AirPort Utility, below), our gigabyte of test files copied to the Time Capsule in 2:11, a dramatic improvement that put 802.11n in the running next to Time Capsule's Gigabit Ethernet performance (which took 1:38) and was well below the 3 to 8 minutes required by wireless configurations only using a single 20 MHz channel.
Of course, connecting the base station directly via an Ethernet cable makes the biggest difference in performance, but also negates the convenience of wireless networking. In any case, the fact that 802.11n wireless networking can approach the ballpark of base station Gigabit Ethernet speeds is pretty impressive. The dark side of the same coin is that the AirPort Extreme and Time Capsule have relatively poor Gigabit Ethernet performance (as noted in the next segment).
It also needs to be pointed out that WiFi performance will degrade rapidly as the user loses signal strength; the poor performance of the first tests were exaggerated by a drop in signal strength related to unknown environmental factors. During the first tests we ran, the AirPort software reported a signal strength that fell from 130 to 117 or below. With a 300 Mbit/sec, 40 MHz wide channel network, the loss in signal reception coverage might offset the faster data rate, or require more base stations to extend the same signal coverage.
If you're thinking that configuring wireless networking sounds a lot more like voodoo than engineering, you might be right. Experimentation to suit your own needs related to signal reception area versus data speed, and accounting for the type of barriers or sources of interference in your specific setup is essential to gain the best possible performance.
The next segment in this series will look at our actual test results comparing wireless performance between modern 802.11n devices, older computers that only support 802.11g, and systems directly connected over Ethernet. We'll also compare performance of 10/100 Fast Ethernet offered by last year's AirPort Extreme, and the Gigabit Ethernet performance of currently shipping Time Capsule and AirPort Extreme base stations, and compare how the base stations stack up against a dedicated file sharing server.
Previous articles related to Time Capsule and its AirPort Extreme cousin:
Exploring Time Capsule: theoretical speed vs practical throughput
Exploring Time Capsule: how it fits into Apple's AirPort family
An in-depth review of Apple's 802.11n AirPort Extreme Base Station
Apple Time Capsule unboxing and preview
A Look Inside Apple's New Time Capsule
Answers to Time Capsule reader questions
Our real world testing of Time Capsule's WiFi performance suggested two findings. First, wireless networking performance can and will vary all over the map even without any obvious variables changing. This makes it difficult to accurately profile the speed of a wireless configuration. In comparison, file copy times over Ethernet or direct connections such as USB were easy to verify in additional follow-up tests. Actual results for wireless throughput will vary dramatically in relation to obvious sources of radio interference in addition to other sporadic factors that are harder to identify.
Second, users with multiple base stations should ideally connect the computers that will be making heavy use of file sharing to the base station actually hosting the shared drive. This requires some network planning, as client computers will attempt to connect to the base station supplying the strongest signal of all the base stations that are on the same network. In other words, locate the Time Capsule or AirPort Extreme hosting the share drive closest to the systems that will be using it the most, and use any additional base stations to extend the network signal elsewhere.
Next, evaluate the wireless network signal strength within AirPort Utility (below) to make sure there are no obvious sources of signal interference. This could include radio emitting devices such as cordless phones and microwave ovens, unnecessary Bluetooth devices that could be turned off, and any metal barriers that might obstruct the signal. Neighboring WiFi networks may also likely impede ideal connectivity, so if possible, experiment with different WiFi channel settings to situate your wireless network outside of the signal range used by other nearby networks.
802.11n WiFi and The 5 GHz Band
As noted earlier, with WiFi 802.11n on the AirPort Extreme and Time Capsule, you can set up your network to use a different set of frequencies all together by selecting "802.11n only (5GHz)" as the radio mode in Wireless settings (below). This isolates your network from interference from other 802.11b/g WiFi networks as well as any 2.5 GHz cordless phones, but of course prevents older 802.11b/g clients from connecting to your network, including most Macs earlier than 2007 and other WiFi b/g devices such as the iPhone or iPod Touch.
If you have both old and new wireless devices, you can cable (via Ethernet, below) a new 802.11n base station hosting a 5 GHz network to an older 802.11b/g base station configured to operate in the "802.11b/g compatible" 2.4 GHz band. This enables faster devices to connect at full speed with minimal interference, while also allowing older devices to connect to the same network through the older base station and interoperate together with every other device on the same network. This setup also prevents 802.11b/g devices from temporarily slowing down a 802.11n network as they transmit, which happens when using mixed devices on a 802.11n base station configured as "b/g compatible."
Incidentally, there is also an 802.11a standard, which is essentially 802.11g running in the 5 GHz band. All of Apple's 802.11n base stations and wireless cards now backwardly support 802.11a/b/g, but Apple never directly supported the earlier 802.11a standard in its products prior to 802.11n because 802.11a was largely intended for office deployments, where the downsides to the 5 GHz band could be more easily worked around. Which brings us to the potential drawbacks--and advantages--of using 5 GHz.
On Page 2 of 2: The Pros and Cons of 5 GHz; Use Wide Channels For a Big Boost.
The Pros and Cons of 5 GHz
As noted by Glenn Fleishman in the article Wi-Fi Networking News: 5 GHz or Bust, the 5 GHz band has much greater radio spectrum available; there are 12 non-overlapping channels, each with 20 MHz of bandwidth. The entire 2.4 GHz band is only 80 MHz wide, which only allows for three non-overlapping 20 MHz channels; while you can select any channel between 1 and 11 in the standard 2.4 GHz band, there is so much overlap between channels that only 1, 5, and 11 can really coexist in the same area without interference. When using 5 GHz, the base station selects the channel for you automatically.
However, 5 GHz is also a higher, shorter radio frequency, which means that at the same amount of radio transmission power, its radio waves propagate shorter distances than those of 2.4 GHz base stations. The 5 GHz band is also worse at penetrating solid objects such as wooden walls in a home (neither band can penetrate metal walls, such as lath and plaster walls using a metal mesh found in some older buildings). There are also power transmission restrictions that affect the use of the 5 GHz band. These factors combine to result in users likely seeing a significant drop in their signal range when using 5 GHz.
In our initial tests, switching to 5 GHz initially had no positive impact on wireless transmission speeds. In fact, it actually seemed to slow things down. However, Apple's 802.11n AirPort devices, including Time Capsule, support a wide channel mode when using 5 GHz that does make a big difference in network speed.
Use Wide Channels For a Big Boost
The greatest advantage to using 5 GHz is the ability to bond two channels together, which Apple calls "Use wide channels." (below) This allows the base station to grab twice as much radio bandwidth (40 MHz) and should be turned on by default when using the 5 GHz band. This will also boost the reported connection speed from 130 to 300 Mbit/sec, at the expense of possibly interfering with other nearby 5 GHz networks, giving up some signal range, and dropping compatibility with 802.11b/g devices.
However, once configured to use wide channels in the 5 GHz band (the setting hides behind the "Wireless Options..." button on the Wireless tab of AirPort Utility, below), our gigabyte of test files copied to the Time Capsule in 2:11, a dramatic improvement that put 802.11n in the running next to Time Capsule's Gigabit Ethernet performance (which took 1:38) and was well below the 3 to 8 minutes required by wireless configurations only using a single 20 MHz channel.
Of course, connecting the base station directly via an Ethernet cable makes the biggest difference in performance, but also negates the convenience of wireless networking. In any case, the fact that 802.11n wireless networking can approach the ballpark of base station Gigabit Ethernet speeds is pretty impressive. The dark side of the same coin is that the AirPort Extreme and Time Capsule have relatively poor Gigabit Ethernet performance (as noted in the next segment).
It also needs to be pointed out that WiFi performance will degrade rapidly as the user loses signal strength; the poor performance of the first tests were exaggerated by a drop in signal strength related to unknown environmental factors. During the first tests we ran, the AirPort software reported a signal strength that fell from 130 to 117 or below. With a 300 Mbit/sec, 40 MHz wide channel network, the loss in signal reception coverage might offset the faster data rate, or require more base stations to extend the same signal coverage.
If you're thinking that configuring wireless networking sounds a lot more like voodoo than engineering, you might be right. Experimentation to suit your own needs related to signal reception area versus data speed, and accounting for the type of barriers or sources of interference in your specific setup is essential to gain the best possible performance.
The next segment in this series will look at our actual test results comparing wireless performance between modern 802.11n devices, older computers that only support 802.11g, and systems directly connected over Ethernet. We'll also compare performance of 10/100 Fast Ethernet offered by last year's AirPort Extreme, and the Gigabit Ethernet performance of currently shipping Time Capsule and AirPort Extreme base stations, and compare how the base stations stack up against a dedicated file sharing server.
Previous articles related to Time Capsule and its AirPort Extreme cousin:
Exploring Time Capsule: theoretical speed vs practical throughput
Exploring Time Capsule: how it fits into Apple's AirPort family
An in-depth review of Apple's 802.11n AirPort Extreme Base Station
Apple Time Capsule unboxing and preview
A Look Inside Apple's New Time Capsule
Answers to Time Capsule reader questions
Comments
Thanks for the timely info! I've been thinking of going N (5 Ghz) to avoid my building's crowded 2.4 spectrum. My needs are short-range, so I think I'll go for it!
Yeah I already got a Airport Extreme Router it just I really don't have a lot of 802.11n products yet. I wanted to do 802.11n but I got the Mac Mini and iPhone plus a Netgear print server for my three HP 8450s. I wanted to buy two 1TB Time Capsules and now a two Airport Express Base Station that's 802.11n. I can connect that to the Time Capsule to the ethernet and use it as 802.11b/g ONLY and have everything else 802.11n ONLY. Then I can replace that Netgear print server with a 1TB Time Capsule. Then I really would have a 802.11n House with support for 802.11a/g without slowdown!
Sure, I've got 4 disks taking that data, and I've got a whole lot more ram for disk caching, but 15 seconds vs. 98 seconds is pretty sad. I've got a kurobox that is also slow, and that drove me to build a real honest to goodness file server, I'm glad I did. To be fair, the time capsule is really a repository for time machine, and as such, speed doesn't really matter.
Sheldon
How tough can it be to spell words correctly? Or open a dictionary? There are many out there.
It's "separate." There is no excuse for getting it wrong.
</cranky>
Dismal gigabit ethernet performance is right! I've got a linux box configured as a server with a 5 disk raid array and I copied about 1 gigabyte worth of files (office 2003 and office 2007 images for bootcamp) to my linux box from my macbook pro via gigabit ethernet in about 15 seconds.
Sure, I've got 4 disks taking that data, and I've got a whole lot more ram for disk caching, but 15 seconds vs. 98 seconds is pretty sad. I've got a kurobox that is also slow, and that drove me to build a real honest to goodness file server, I'm glad I did. To be fair, the time capsule is really a repository for time machine, and as such, speed doesn't really matter.
I think you're being unrealistic.
I've found that the storage on both ends matter. You are copying from a notebook hard drive, so I think your results are pretty impressive. Even when both ends have 10k or 15k hard drives, I've found the drives to be the limiting factor.
Problem is, I have absolutely no problems or speed issues running the wireless in b/g so I can't justify the investment.
This article is part 3 of 6? Time Capsule is a nice product, but I don't think it deserves this level of attention.
Then ignore it, I found this article very informative. It concerns Airport Extreme too.
I'm 10 feet away from the base station and there's nothing interfering with the signal.... well... someone is talking on the cell phone, but I doubt that would slow it down *that* much.
I'd like a comparison between the Apple product and competing N products. I'd be curious to see which one is the fastest. I think I already know which one is the easiest to configure... but I'd let this ease of use go in second place if wireless and Gigabit speeds are not to par.
http://review.zdnet.com/wireless-acc...-32902549.html
Assuming the extreme performs more or less the same as the Time Capsule it was the 2nd fastest N router behind the D-Link DGL-4500 "Xtreme Gaming Router" in a N only environment and middle of the pack for a mixed environment.
The express is rather pokey though. But given the think looks like a power brick and plugs into the wall I dunno that I'm surprised.
Er, we have several non-n Intel Macs and they all support 802.11a.
I've just moved the network over to it due to a very busy 2.4 GHz in our area - and the N computers not connecting to the AEBS after the 7.3.1 firmware update in b/g compat mode.
Seems snappier, but no objective tests. So the computers are happy - I have an older Belkin I resurrected for the remaining gear (PowerBook and iPhones - G only, Wii - B only, Nintendo DS's B/WEP only) - my ghetto network.
The stuff that moves files, video, etc. is all on the A network, and it seems all lovely.
Cheers,
Martin.
My Netgear router was $119 at Fry's and it operates 2 channels simultaneously - 5ghz for wireless N and 2,4ghz for wireless a/b/g.
The other thing I don't like about the Airport is that it requires software installed on your computer to operate. If you want to change a setting you either have to be at that computer, or be running Remote Desktop.
I had bought a gigabit Airport Extreme and retuned it the next day. It's uncharacteristic of Apple to make something more complicated that it's competition.
At my office, I jumped on the Airport Extreme within a week of it going gigabit. We bought three of them, and mounted them upside-down on the ceiling of the first floor - one dead center at 5ghz, wide channels, two others to the front and back of that one about half way to the walls, using 2.4ghz b/g only. The b/g's are configured identically to provide roaming for our many older clients. All of them are cabled directly to our gigabit backplane. The building is about 25,000 square feet, and every nook and cranny of the first floor is completely bathed in signal. The older 2.4 ghz network punches right through the floor to the basement. The 5ghz network does not, but it still isn't impeded in the slightest by walls or dividers on the first floor. I've placed 3 graphic designers on the 5ghz network now, and while copying large files to or from their file server all in one go is slower, that isn't their typical usage pattern. None of them can really tell the difference in their day-to-day work. It's brilliant. Our wiring closet is now officially deprecated.
Let us know how many workers develop WiFi tumors.
This will become our prime wireless network - linking my MacBook and the AppleTV to the hardwired network. After set-up with all the names, parameters, security notes, etc. from the original Airport Express, I will take the latter and wipe it and set it up anew limited to G&B.
I always have to slow things down and lower the security settings to get a couple of regular guests with slow XP machines onto the network. This should allow me to keep them on the new, slower network - and keep on cranking my goodies at N.
We have a couple new wireless networks in the neighborhood - though only one is N. I'll probably try the 5ghz trick, as well.
Even though I've been a geek for decades, networking is still alchemy afaic - but, if it all works, I'll drop by make a few notes.
--------
Got nowhere, yesterday. Today, found a forum that passed along the suggestion that I use "bridge" to define my original Airport Extreme - of course, leaving the Time Capsule to automatically assign DHCP. Seems to have done the trick.
My father-in-law [5th-wheeler parked out in the driveway] is ensconced in the guesthouse - his old XP laptop running 80211.b is talking to the AE which is only broadcasting b&g. Had to leave the security set down to WEP since his laptop is aghast at WPA2. My wife also runs her G4 ibook from the same router.
Meanwhile, AppleTV, MacBook, iMac [though normally ethernet] all access the Time Capsule just fine at 80211.n/5ghz.
I've found it pretty good on Intel though.